1. Field of the Invention
The present invention relates to networks and more particularly, to a system and method of controlling network traffic data in a full-duplex switched network operating according to Ethernet (IEEE 802.3) protocol.
2. Background Art
Switched local area networks use a network switch for supplying data frames between network stations or other network nodes, where each network node is connected to the network switch by a media. The switched local area network architecture uses a media access control (MAC) enabling a network interface within each network node and the network switch to access the media. The network switch stores and forwards data frames received from a transmitter node to a destination node based on header information and the data in the received frames, including source and destination address. An external memory, such as an SSRAM, is used by the network switch to temporarily store the data frames as they are passed through the switch. In particular, the network switch stores and fetches data frames in the external memory via an external memory bus.
A difficulty in designing a network switch to be “non-blocking” (i.e., preventing delay in transferring a data packet received at an input switch port), yet with limited memory bandwidth resources, is ensuring that each port of the network switch has sufficient memory resources allocated from the external memory to prevent the delay of data transmission. The external memory bus of an SSRAM, for example, has a limited bandwidth based on the number of data bits on the external memory bus (e.g., 16-bit, 32-bit, etc.) and the data rate of the bus. Hence, a network switch may allocate a fixed number of time slots for each port of the network switch. However, the data traffic on higher speed switch ports may exceed the bandwidth capacity of the external memory bus.
Previous switches have been proposed which assign memory slots to ports using a request based arbitration scheme that grants memory slots to ports requesting slots on a “first come, first serve” basis. As the slots are requested, an arbitrator grants slots in answer to the requests as they are received, but only after previously requested slots have been completed. The request based arbitration scheme, however, is complex and difficult to implement, increasing the likelihood for errors. From an implementation standpoint, such arbitration schemes present more difficulty in controlling the memory allocation.
Other systems have included fixed slot schemes which assign a fixed amount of bandwidth to each slot of the network switch. However, these systems are expensive since sufficient bandwidth capacity must be provided to all of the slots at all times. In addition, since ports are not fully utilized at all times, much of the assigned bandwidth is wasted due to times of inactivity on a network switch port.
There is a need for a network switch that assigns memory access slots according to a programmable memory slot assignment scheme to avoid waste of bandwidth resources.